Production of sodium bicarbonate and ammonium chloride in modified ammonia-soda type process



Jan- 19, 1954 w. s. MILLER Erm. 4

PRODUCTION OF SODIUM BICARBONATE AND AMMONIUM CHLORIDE 1N MODIFIED AMMONIA-SODA TYPE PRocEss Filed sept. 1s, 1952 ATTORNEYS Patented Jan. 19, 1954` .srA'rss iai-,ENT 1 oFF-Ice L l $666,686 f K' moDUofrIoNf for. soDiUM BloAnBoNsfrE AMMONIUMoHLoRIDE IN MODIFIED .AMMONIA-SODA TYPE PROCESS Warren "Standish *Millen Houston, Tex., and. `r liouisc. Hirdle'r, Maplewood, La., assignors to -MathiesonrlChemicaJ Corporation, a corporay .tion of Virginia and with carbon dioxidel obtainedl ordinarily from-the calcination ofiimestorie. .The 'sodium bicarbona-tefis crystallized,r out of solution and ordinarily lis l converted by calci-'nation to sodium carbonate,y the carbon dioxide 'produced being utilized in the carbonation step yof the process.`

The liquor lren'iaining .after'the separation ofthe sodium bicarbonate contains axrlmonium ohioride in reddition. .to-:ammoniumbicarbonate :and sodium chlorideA i made toaworis upthe mother liquor. 4to :separate ammonium eliloi'ide'V in solidform '.so that 'the residual .liquida-may be used Aagairrfor tliefprepa-V ration of sodium bicarbonate. However, oommercial operations of the ammonia-sodazprocess conventionally treat the liquor'remaining after bico .rboriat-esepati-ationY Awith lime, iobtain'e'd 'from thefcalc-nationof limestone, viri Aorder :to recover ammonia- .which isf utilized the namnuiriiation stepsofthefprocessjfand ultimately discard a porition of rthev usablezsaltland V`all of the chloride E io as calcio-m. chloride'.

Inour `application Serial No'. 248,190 filed September 25,` 11951now U. S. Patent No. 2,622,904,issued'December 16, 1952, We disclosed a cyclic tvvoestage' 'process' characte'rized by pars ticular operatirigzprocedure and 'limiting' conditions, Vwhich provides apro-cess of 'commercial feasibility fby .producing both :sodium bicarbonaterandainmonium :chloride rin ygood yield and qualityfin aiexible operationV Withoutneed of refrigeration, evaporation for us'eoi contaminatiingnrextraneouspreoipitatingageiits; The proc ess. .isfehanaoterizedby A'cstaiollsliuit;''a `cycle wherein Iau' aqueous :liquor contamina sodium,

vMany yatte'il'lpts have been i 1 ammoniumcliloride, hydroxide and -bicarbouate` ions is circulated between a sodiumbicarbona-te producing stage and an vammonium chloride producing stage and'rin which'the coinposihon of the circulating rliquor 'is' controlled by split addition of the ammoniarequired iii-a particu? ylar manner while adding the usualequi-molar': quantities of'sodium chloridein the'iorm fof the ammonium chloride producing staigeand less'- thanthe mola-r requirement of make-up .water for a complete cycle'is added. Approximately half but less than'the molar requirement of ain--1 monia lfor the ldouble decomposition reactions or the complete'cycle falso is :added to the circulating liquoruntil 4the ratio or bicarbonate to the sum or bicarbonate and hydroxide ions is vabout 0.37 to 0:42. Sodium chloride in the *formof solid salt is added to the "circulating liquor and the temperature of the liquor is controlled at about 20"to 40 C.' while dissolving the saltl and separating lcrystallized ammonium chloride. The lremaining .make-up water and ammonia are added to the circulating liquor which lis then circulated to vthev s'odium'bicarbonate producing stage'. y

The cyclic process is `particularlyV "advantae geous in that both `sodium 'and chlorine values are recovered in useful form while producing good 'yields of sodium'bicarbonatev and 'ammonium chloride `oi' high quality. Moreover, the needfor refrigeration,evaporation or usefof coritaminating Vextraneous precipitating Aagents 'is eliminated. The chief problem of operation of the cyclic process, however, is that it requires a close control of solution composition because 'or its cyclic nature.k Also, in this Aprocesscertain solublepiinpuritiesfsuch as sodiumsulia'te, mayv be introduced with thelzsolidgsalt 'which shouldbe 'removedfbeiore they build' up' V.to vexcessive l. concentrations, Thus although the process can high yields of goed quality. sodium bicarbonate.

We have now found that operating the twostage cyclic process in a deliberate state of unbalance produces an excess of solution over that.'`

Vof the starting solution which can be advan` tageously utilized in a conventional ammoniasoda process, and which also can be advantageously used to control impurities, while maximizing sodium bicarbonate yield .Without undue loss of ammonium chloride yield. Operating flexibility is thus introduced into `the cyclic process.

Our cyclic process is chiefly characterized by the addition of more than the molar, requirement of water for a complete cycle inthe two-stage process in which the composition of the circulating liquor is controlled by split addition of the ammonia required in a particular manner while adding solid sodium chloride and carbon dioxide and removing sodium bicarbonate and ammonium chloride.

It is particularly desirable as a practical matter to operate the cyclic process in conjunction with the conventional ammonia-soda process as the ammonia-soda process oiiers a means of ainmonia recovery and a cheap source of carbon dioxide from its lime kilns. Thus, existing equipment of the ammonia-soda process may be advantageously utilized in our cyclic process to provide carbon dioxide and to recover ammonia from reject excess solution of `the cyclic process. Moreover, bleeding 01T the excess solution produced by the addition of excess water advantageously removes impurities and can be used to control the amount of impurities in the cyclic system.v The concentration of an impurity, such as sodium sulfate, is advantageously controlled byadding enough excess Water so that the quantity of sodium sulfate added per cycle with the sodium chloride is exactly equivalent to that bled out in the excess solution. Thus, the sodium sulfate may be allowed to build up to an operable concentration and kept at that concentration by removing any sodium sulfate added during the cycle in the excess solution removed. The quality of the solution is such that it can be processed in an ammonia-soda process. 1

The quantity of excess solution may be vconsiderable in commercial operation, for example 10 per cent of the plant capacity, and substantial cost savings are realized in utilizing the solution in the ammonia-soda process. Thus', by combining the cyclic process and the ammoniasoda process the highest yields of high quality products are obtained and reject materials are effectively utilized. Y

According to our invention, a cyclic two-stage process for production of sodium bicarbonate and ammonium chloride from solid salt, carbon dioxide, ammonia and water is provided in which an aqueous liquor containing sodium, ammonium, chloride, hydroxide and bicarbonate ions is circulated between a sodium bicarbonate producing stage and an ammonium chloride producing' stage. Carbon dioxide is added to the ambicarbonate producing'stage in an amount producing a ratio of bicarbonate to the sum of bicarbonate and hydroxide ions of about 0.60 to 0.80, and the temperature of the liquor is controlled at about 28 to 60 C. while separating crystallized sodium bicarbonate. The recovered liquor is circulated to the ammonium chloride producing stage, and less than the total amount of make-up water to be used is added, the total amount being more than the molar requirement for a complete cycle. Approximately. half but less than the molar requirement of ammonia for the double decomposition reactions of the corn- `plete cycle also is added to the circulating liquor until the ratio of bicarbonate to the sum of bicarbonate and hydroxide ions is about 0.37 to 0.42. Sodium chloride in the form of solid salt is added to the circulating liquor, and the temperature of the yliquor is controlled at about 20 to 40 C. whiledissolving the salt and separating crystallized ammonium chloride. The remaining make-upV water and ammonia are added to the resulting liquor which is then circulated to the sodium bicarbonate producing stage.

In our'process, an excess of solution remains over that of the starting solution and is bled out of thecycle eithery after the sodium bicarbonate producing stage or the ammonium chloride producing stage. The excess solution is bled off and charged to a conventional ammonia-soda process that is operated in conjunction with our cyclic process, for further processing or to recover ammonia. The excess solution may be introduced into various stages of the ammoniasoda process. For example, if the excess solution is bled 01T after thel precipitation of ammonium chloride it is desirable to introduce the solution to the carbonating step or the ammoniation step to recover sodium bicarbonate. If the excess solution is removed after the precipitation and removal of sodium bicarbonate, it is ldesirable to introduce it into the ammonia recovery system of the ammonia-soda process.

The process of our invention produces an excess solution which can be utilized in a conventional ammonia-soda process and therefore permits an integrated operation for producing sodium bicarbonate and-ammonium chloride, in which a cheap and available source of carbon dioxide and existing plant equipment can be utilized. Moreover, the excess solution provides an effective means. of controlling the concentration of undesirable impurities in the cyclic process by removing them from the cycle while maintaining good yields of ammonium chloride and sodium bicarbonate.

The total amount of water required in the process of our invention is more than the molar requirement for a complete cycle and may be added in one amount or in successive portions. The amount of Water inY excess of the molar requirement is not critical. For example, about 5 to 15 per cent is an advantageous practical range. However, too much excess Water will decrease the recovery of ammonium chloride and the practical upper limit is governed by this factor. For example, in the ammonium chloride producing stage when excess Water is added before or as crystallization of the ammonium chloride occurs the excess water becomes saturated with sodium chloride and ammonium chloride. Therefore, part of the sodium chloride added and also part of the ammonium chloride which previously would have precipitated, must now go to saturate the excess water. The recovery of ammonium chloride is therefore reduced very slightlyg-fwhilefthes consumption ofJ so.dium..ch1oride-: isi increased sliglitly; for; example, about: 5toif20=pen centra, over: that,- ofl'a/.cycleeusing only;l thermolarrequirement of; water.

Ass-theevolume of? solution is now.- increa'sed. sliglfitly,E thee, confiposition--y of thef'solution; is? also`-` changedi slightly.- dueretorthe; largen quantity: ofi sodium. chloride? and ammonium` chloridernow., present-fin relation"v to" thei samefamount- -fofahyz-w droxidel. and@ bicarbonatev ions present.` After." i crystallization ofs ammonium? chloride;;asi` the. Volume-of. :solution: isi-greater. and. asi the comeuosition of:- the; solutionf is slightly differente, a; slightly larger quantity of carbon dioxidefandf vammonia than in a cyclic system usingfonlytli'e molarv requirement of 2 water; mustabe f added .in order to f endzup, with. a. solution; afterrprecipitaef tion.- off.' sodium bicarbonate;y of. exactly; thes samez: composition. or. ionic-rat.?os.-4 asfbeforez. The: Vol1 ume .of the final-solution is, oA course; stillngreaster:z

thanthei.startingsolutionrand'ithef:excesszmam'beitf .removedrat this pointa. 'Ehefyield ofsodiumvbie carbnnateja.v isfx slightly; increased dueftbrtheilarger; quantity. of lsolutioncarbonated.

` In.the..process.of our. invent-ionr it isaparticuf4 larlyf desirable; to operate with aftemperature fof. about. 40? to.- 605 C. in the. sodium. bicarbonate."- producing ,stage andl atemperature--of about 20 130.35? CVin the ammoniumrchlorideproducingi stage. llt'isalso particularly desirable-tocontrol.. the .rise.in the Aratio of. bicarbonate tor the sum of g bicarbonate. and; hydroxide. ions by carbonation in the. sodium..bicarbonate.producing stagel to aratioofzito 0.67 andto.controldzhereduce:`

non in. the. ramoty. amnicniaadeinoninthe. 35"- all v Accordingeto` our.. inventiem. the 1 ratio; .ayothef GS solution .resulting from fthe; precipitation aand-:filaA tratiofnof4 ammonium.. chloridec-thenzisfcontrolled, f betweenabout..0.37, and.. 0.4:2:` but preferably.. bee tween.0.38.and 0.40, by; split..additionfofftheeani-u moniato.,the,circulatedtliquor,'.irnpartaiollowingg carbonation .and sodium.. bicarbonate.- separation and'finV p art following the..solid saltadditionaande ammonium chloride. separation. After.. the rstep.. of" washing the` ammonium. chloride cake andi.

adding ammoniatoihelltrate, carlrionation adr 7n;-

vantageously is carried to about z.=0'.(i0.to..0.8(1,...A but preferably. about .a+-0.6.2 or slightly Ahigher 5*. to;.be-addedcan.beisplit; andapproximatelyfhali of.r thefA water: to.. be added-i then. is. available;at;` each-end-of thegcycleor Washing. the'gprecipitated salts. In; many; other: suggested. processes: for: separating ammonium.. chloride nearly" all.; therl Water; must; be. added*y in. the; carbonation?. step; leaving-:little or. nonev for washingztheibicarbone aterca'ke'.

In operationt accordingfto our invention-armati:`

' varyfrom@ about 0.50.' to:` 0.80 and: 111;. fromabouti:

I 0i05: to;=0.f55fin .rthedliquor from. which ammonium:

chloride: has. precipitated: as the; temperatures-v varies,` 205" totv 45m C:. In theY liquorffromi bicarbonate? precipitation. may# vary1 fromA O'EGI-f l tos0g95randryffrom. 0.05L-to.'0`.4' as the temperaturen 'Bh-ev; operation 1z,according toH ourinvention will be'efurtherillustrated by reference to" theac'corm'--V panyingdrawing" which` represents' a schematict floxwdiagramz of a" cyclictWo--sta'ge-1processf operat ated; in; conjunction withv aconventional" anr-VU monia soda process;

In the.' drawing: the'- aqueous^ li'quercirculates;ly

contnuouslyfifom thevammonium chloride lter .f lil through making tower I4 to sodium bicarbon-n atai'lter'Ifliandthen'1througli mixingtank 22,- coolingequipment 25 and mixing'tank- 2T' back; to: filters lil; The'. addition ofa part of'tlie'fvree' quired?. markeup Water" is'I shown diagrammati-Y ca-llyfthroughfline il 2to1thefliduor'recoveredfiomil filter?msanducirculatingin line- Ill. The Water-s is.- advantageously addedl in the-'formY ofC Wasleings from; the; crude ammonium chloridefilter caller separated` by'illt'er l0; Ammonia; is'fadded'` tothe. liduorrcirculating#through linel I lciyfmeans:y of.Ik connection r3.1. The circulating liquor ischarged. to; making towerA I4 to which carbone dioxide iis; charged a'si indicated by means offline i 5; Temperature control" provided-in theusualf flmanner in the making tower I4 to prevent` ai" temperature rise.. above about 60 C. The bicarf bonate liquor is\.vcirculated through line lli-toid filter i1 for removal of crystallizedsodium biliar-l bonate` The crudefsodium bicarbonate may'bery passed after vwashing in the usual mannlerfto'` calciner i 8 for production of soda ash. d Wat'erds added? to .the 'liquors recovered'ffiom :lterrl'lwand; circulating through` line'f lgf-fby means`l of'zconnectionfdls. Againthewaterfisfaddedfinitheff form ofi washngs from: tZr1e-Crude sodiuml bicari-l bonatei=lterx cakef. Ammoniaisf added to'rtlie liquorccirculatingfin line?. ES lby meansf ofi'con'nec- Y tionzf2zi Sodiumchlorideinithefform of tliesolidsa'ltiis addediasindicated b'yflineZ3- to the aqueous@ after eithenprecpiftating step: Eor'exarnple; tle

excess.. solution .may be removed from i line lil by?- f conventional-...amm onium-.soda-process :operate'dsim coniinaction with cyclicv nroicess for` further" processing, on to;,-rec'oV-er l ammomaa For.y example;

the, excess., solution. inayf be? intmducedr into: theTlv carbonatiom. ammaniation orf ammonia. recoverye' in'A the 'ammonia-soda process may be used for producing the sodium bicarbonate. In the operation of our invention, the temperature rise due to the ammoniation step prior to carbonation and the carbonation itself is employed to bring the temperature of the liquor to the desired range for ltering the sodium bicarbonate. Undue temperature rise is avoided and temperature is readily controlled in our process by means of the usualcooling facilities operated in connection with conventional making towers. The bicarbonate lter liquor then can be cooled with ordinary cooling water in conventional cooling equipment to the temperature desired for ammonium chloride precipitationy and filtration. As shown in the drawing, the cooling appears to follow the salt addition, but it may be desirable to precool the bicarbonate iilter liquor to the temperature desired for ammonium chloride precipitation, e. g. 30 C., before the addition of salt. After the addition of salt, ammonium chloride begins to precipitate and a smaller amount of additional cooling then is required to maintain the desired temperature.

Our process will be further illustrated by the following example:

In a solution having the molar composition indicated below and starting at a temperature of about 40 C., water used in washing a previous precipitate of sodium bicarbonate is added in the specied amount. The total amount of Water added in both stages is about 10 per cent more than the molar requirement for a complete cycle. All lat once or in successive portions, the specied amounts of solid sodium chloride and ammonia are added. The water, solid salt and ammonia may be added together or separately. The mass is cooled to Iabout 30 C. and stirred. The sodium chloride goes into solution and ammonium chloride crystallizesout according to the following equation:

Solu. I Soin. II 130.6 N H4 95.8 N H4 44.2 Na 35.4 NaCl (solid) 79.6 Na 20.2 H003 17.9 NH3 20.2 H003 34.8 NH4C1 154.6 Cl 25.1 H20 155.2 Cl (solid) 12.4 NH3 30.3 NH2 978.6 H2O 1003.7 H2O The ammonium chloride is separated by filtration or centrifuging. The solution, having the molar composition indicated below, is then used son. 1I som' I 11 a7 4 co 121i H 4 a 2 i a 20.2 Hooi 19.5 NH. 26.3 Hoo 352 NBHCO@ 155.2 o1 {16.0 i1o} 155.2 o1 a l 2.1 NILHCOJ` 30-3 NH3 12.4 NH3 1006.7 Hgo 982.6 H20 The temperature rises due to the heat of the reaction. It may be permitted to rise above 40 to as high as C. but in this example the temperature at the completion of the reaction is to be about 40 C. It may be subsequently cooled to 40 C. as the reaction is completed, however, or the temperature may be controlled by cooling so that the solution does not exceed 40 C'. 'Ihe sodium bicarbonate is separated andthe solution used to continue the cycle.

,-It will be noticed that in this cycle a larger volume of solution exists (more Water present).

after precipitation of both the ammonium chloride and sodium bicarbonate than in the cyclic process described in our application Serial No. 248,190, now U. S. Patent No. 2,622,004, issued December 16, 1952. Thereforaaccording to our invention, this excess solution can be bled off at either point of the cycle. By bleeding off this excess solution impurities build-up is prevented but the quality of the solution is such that it can be processed advantageously in a conventional ammonia-soda process operated in conjunction with our cyclic process with substantial mutual advantages.

We claim:

1. A combination process for the production of sodium bicarbonate and ammonium chloride from sodium chloride, carbon dioxide, ammonia and water, which comprises circulating an aqueous liquor containing sodium, ammonium, chloride, hydroxide and bicarbonate ions between a sodium bicarbonate producing stage and an ammonium chloride producing stage, adding carbon dioxide to the ammoniated salt-containing liquor in the sodium bicarbonate producing stage in an amount producing a ratio of bicarbonate to the sum of bicarbonate and hydroxide ions of about 0.60 to 0.80, controlling the temperature of the liquor at about 28 to 60 C. While separating crystallized sodium bicarbonate, adding less than the total amount of make-up water required, the total amount of water required being more than the molar requirement for a complete cycle to the liquor which is recovered and circulated to the ammonium chloride producing stage, adding approximately half but less than the molar requirement of ammonia to the circulating liquor to produce a ratio of bicarbonate to the sum of bicarbonate and hydroxide ions of about 0.37 to 0.42, adding sodium chloride as the solid salt. controlling the temperature of the liquor at about 20 to 40 C. while dissolving the salt and separating crystallized ammonium chloride, adding the remaining make-up water and ammonia to the liquor recovered, circulating the liquor to the sodium bicarbonate producing stage, removing liquor from the circulating system in excess of about the amount originally circulated between the sodium bicarbonate producing' stage and the ammonium chloride producing stage, separately7 ammoniating in an ammonia-soda" process a separate aqueous solution of sodium chloride. carbonating the ammoniated solution of sodium chloride by adding carbon dioxide, separating sodium bicarbonate from the carbonated solution and recovering ammonia from the liquor from the sodium bicarbonate separation step by adding lime and introducing the liquor removed from the circulating system in excess of about the amount originally circulated between the sodium bicarbonate producing stage and the ammonium chloride producing stage into at least one of the steps of ammoniation, carbonation and ammonia recovery in the separate ammonia-soda process.

2. The process of claim l in which the liquor in excess of about the amount originally circulated between the sodium bicarbonate producing stage and the ammonium chloride producing stage is removed after the sodium bicarbonate producing stage.

3. 'I'he process of claim 1 in which the liquor in excess of about the amount originally circu,

latedbetween the sodium bicarbonate producing stage and the ammonium chloride producing stage is introduced into the carbonation step of the ammonia-soda process.

6. The process of claim l in which the liquor in excess of about the amount originally circulated between the sodium bicarbonate producing stage and the ammonium chloride producing stage is introduced into the ammonia recovery step of the ammonia-soda process.

WARREN STANDISH MILLER. LOUIS C. HIRDLER.

No references cited. 

1. A COMBINATION PROCESS FOR THE PRODUCTION OF SODIUM BICARBONATE AND AMMONIUM CHLORIDE FROM SODIUM CHLORIDE, CARBON DIOXIDE, AMMONIA AND WATER, WHICH COMPRISES CIRCULATING AN AQUEOUS LIQUID CONTAINING SODIUM, AMMONIUM, CHLORIDE HYDROXIDE AND BICARBONATE IONS BETWEN A SODIUM BICRBONATE PRODUCING STAGE AND AN AMMONIUM CHLORIDDE PRODUCING STAGE, ADDING CARBON DIOXIDE TO THE AMMONIATED SALT-CONTAINING LIQUOR IN THE SODIUM BICARBONATE PRODUCING STAGE IN AN AMOUNT PRODUCING A RATIO OF BICARBONATE TO THE SUM OF BICARBONATE AND HYDROXIDE IONS OF ABOUT 0.60 TO 0.80, CONTROLLING THE TEMPERATURE OF THE LIQUOR AT ABOUT 28* TO 60* C. WHILE SEPARATING CRYSTALLIZED SODIUM BICARBONATE, ADDING LESS THAN THE TOTAL AMOUNT OF MAKE-UP WATER REQUIRED, THE TOTAL AMOUNT OF WATER REQUIRED BEING MORE THAN THE MOLAR REQUIREMENT FOR A COMPLETE CYCLE TO THE LIQUOR WHICH IS RECOVERED AND CIRCULATED TO THE AMMONIUM CHLORIDE PRODUCING STAGE, ADDING APPROXIMATELY HALF BUT LESS THAN THE MOLAR REQUIREMENT OF AMMONIA TO THE CIRCULATING LIQUOR TO PRODUCE A RATIO OF BICARBONATE TO THE SUM OF BICARBONATE AND HYDROXIDE IONS OF ABOUT 0.37 TO 0.42, ADDING SODIUM CHLORIDE AS THE SOLID SALT, CONTROLLING THE TEMPERATURE OF THE LIQUOR AT ABOUT 20* TO 40* C. WHILE DISSOLVING THE SALT AND SEPARATING CRYSTALLIZED AMMONIUM CHLORIDE, ADDING THE REMAINING MAKE-UP WATER AND AMMONIA TO THE LIQUOR RECOVERED, CIRCULATING THE LIQUOR TO THE SODIUM BICARBONATE PRODUCING STAGE, REMOVING LIQUOR FROM THE CIRCULATING SYSTEM IN EXCESS OF ABOUT THE AMOUNT ORIGINALLY CIRCULATED BETWEEN THE SODIUM BICARBONATE PRODUCING STAGE AND THE AMMONIUM CHLORIDE PRODUCING STAGE, SEPARATELY AMMONIATING IN AN AMMONIA-SODA PROCESS A SEPARATE AQUEOUS SOLUTION OF SODIUM CHLORIDE, CARBONATING THE AMMONIATED SOLUTION OF SODIUM CHLORIDE BY ADDING CARBON DIOXIDE, SEPARATING SODIUM BICARBONATE FROM THE CARBONATED SOLUTION AND RECOVERING AMMONIA FROM THE LIQUOR FROM THE SODIUM BICARBONATE SEPARATION STEP BY ADDING LIME AND INTRODUCING THE LIQUOR REMOVED FROM THE CIRCULATING SYSTEM IN EXCESS OF ABOUT THE AMOUNT ORIGINALLY CIRCULATED BETWEEN THE SODIUM BICARBONATED PRODUCING STAGE AND THE AMMONIUM CHLORIDE PRODUCING STAGE INTO AT LEAST ONE OF THE STEPS OF AMMONIATION, CARBONATION AND AMMONIA RECOVERY IN THE SEPARATE AMMONIA-SODA PROCESS. 